Referees' union Prospect has given its "full support" to Clattenburg, adding in a statement: "It is now important that the allegations are fully investigated through the proper process as quickly as possible."

All four officials - the referee, his two assistants and the fourth official - wear microphones and ear pieces that allow them to hear what each other is saying throughout the match.

That means assistant referees Michael McDonough and Simon Long and fourth official Michael Jones should have heard conversations between Clattenburg and the players.

Who is Mark Clattenburg?

"Whether handing out red cards or promoting hair-restoring products, Clattenburg has been no stranger to the limelight since taking charge of his first Football League game as a 25-year-old in 2000."